1. Field of the Invention
This invention relates to a paste-form water-containing dishwashing detergent in the form of a suspension of salts in a solution thereof and to its production. The dishwashing detergent according to the invention is intended to be used in particular in institutional dishwashing machines, as used inter alia in canteens, hotels and hospitals, although it may also be used for other cleaning functions.
2. Discussion of the Related Art
Thixotropic and non-thixotropic pastes have been known for years in the field in question. Thus, EP 75 813 describes a machine dishwashing detergent in the form of a thixotropic paste which has a viscosity of 70 to 200 Pas and which, in addition to polyphosphates, alumosilicates, hydroxides, silicates and carbonates of sodium, contains a thickener from the class of swellable layer silicates. This patent application is more or less directed to the use of the thickener mentioned, i.e. the swellable layer silicates, in such formulations. There are many other prior art publications in which thickener-containing dishwashing detergents are described, cf. for example the prior art discussed in EP 331 370 B1 (Unilever).
However, the use of such thickeners in paste-form, dishwashing detergents is not entirely desirable in practice. Their thickening effect apart, thickeners are expensive and otherwise usually purposeless additives which could be dispensed with on economic and possibly also ecological grounds.
Accordingly, proposals have also been put forward with a view to producing corresponding formulations without the use of thickeners.
Applicant's European patent application EP 0 118 658 A1 describes a process for the production of a paste-form detergent in which alkali metal silicates of the disilicate type are mixed in a certain ratio with alkali metal silicates of the metasilicate type to form detergents with a paste-like consistency.
Similarly, EP 331 370 B1 (Unilever) proposes starting with alkali metal silicates and modifying them by using sodium hydroxide to obtain substantially non-thixotropic pastes. Although formulations according to the two above-cited prior art publications are free from thickeners or consistency regulators, they do contain silicates as a compulsory component. Although silicates are very favorable raw materials in many respects in the field of application under discussion, they can occasionally lead to deposits when used in relatively large quantities and under adverse water hardness conditions and also under certain unfavorable dishwashing machine conditions, with the result that they are not entirely safe to use. In addition, the compounds known from the prior art undergo a rapid increase in viscosity during the production process, so that--with relatively large batches--the end products cannot readily be packed in retail containers and left to harden therein.
Japanese patent application Showa 6245698 describes liquid detergents for use in automatic dishwashing machines which contain 5 to 50% by weight of potassium carbonate, less than 5% by weight of potassium hydroxide and/or less than 5% by weight of sodium hydroxide. The teaching of this citation is based on the observation that, by adding potassium carbonate, the alkaline properties of the detergent remain intact in the event of a reduction in the alkali metal hydroxide content of the detergent. However, pastes are not described; the formulations have low viscosities.
Against the background of this prior art, the problem addressed by the present invention was to provide a detergent for institutional dishwashing machines which would be present in the form of a paste-like suspension of salts in a solution thereof, would be free from thickeners and fillers and which, during its production, would pass through a low-viscosity phase to enable the detergent to be packed in retail containers from large tanks before it solidifies to form a paste. Another problem addressed by the invention was to formulate the corresponding dishwashing detergents which would not contain silicates, such as alkali metasilicates, as a compulsory ingredient.